Understanding network traffic from operational networks is critical to the design and evaluation of network protocols. We present analysis of a data set comprised of eight months of RADIUS authentication data taken from a large national dial-up Internet Service Provider (ISP). We present basic statistics, including session counts based on time-of-day, session length distribution, session inter-arrival times, and growth in the customer base over the measurement period. We investigate more deeply several properties of the data. We use area code information to correlate account location with basic statistics. For example, we find that United States west coast accounts tend to have earlier-than-average mean session start time. We find that 40% of sampled accounts exhibit concurrent sessions (two or more sessions active at the same time), while 20% show multiple originating phone numbers. Both phenomenon are likely to increase as users become more mobile and sophisticated. Finally, we offer evidence of significant session activity due to hypothesized automated processes, characterized by periodic interarrival times and/or constant session durations. Our results provide important data for the simulation and modeling of access network protocols and applications. They may also form the basis for creating a workload model of access networks.